The present invention relates to diesel pre-reforming catalysts for use with diesel to create a methane-rich syngas for fuel cells. Pre-reforming partially completes a steam reforming reaction at a much lower temperature than steam reforming and using a highly active catalyst. Pre-reforming processes convert heavy hydrocarbons into methane-rich syngas. Catalytic pre-reforming typically reforms feedstocks from natural gas up to naphthas. Diesel, however, is an attractive hydrocarbon fuel for fuel cells. Diesel has the advantages of high energy density, well-constructed infrastructure, and safety. While natural gas, liquefied petroleum gas, and the like are converted through pre-reforming relatively easily, diesel cannot be easily pre-reformed. Diesel is a liquid fuel that is a complex mixture of hydrocarbons, including saturates, olefins and aromatics. The wide boiling range of the components creates complexities relative to mixing, evaporation, methane generation, catalyst fouling and fuel input steps that are not at issue with lower weight hydrocarbons.
Solid oxide fuel cells (“SOFC”) use methane and hydrogen, as well as carbon monoxide. SOFC systems are less complex than other fuel cells because they have fuel flexibility. SOFC are capable of internally reforming methane. The internal reforming of methane also suppresses temperature increases in a SOFC stack. Heat generated from SOFC is accumulated in the SOFC stack. Unless the heat is properly released, the temperature of upper cells increases. This can lead to the failures of SOFC, as well as failures of sealant and interconnect materials. Internal reforming of methane is one manner of addressing the heat issue because the reaction by which methane is reformed is endothermic.
Diesel pre-reforming has historically experienced problems with coke formation and low operating temperature activity reduction. Diesel reforming catalysts are readily deactivated by coke formation. These types of heavy hydrocarbons are more prone to coke formation than light hydrocarbons. Coke formation is the main deactivation mechanism of these catalysts. In addition, pre-reforming is preferably operated at lower temperature than other reforming methods in order to encourage methane production. Pre-reforming is generally operated under 500° C. because the presence of methane is favorable at these temperature ranges. However, catalytic activity is typically proportional to the operating temperature. Therefore, the lower the operating temperature, the lower the activity of the catalyst. It would be advantageous to develop a catalyst with high tolerance to coke formation and high activity under 500° C. as a diesel pre-reforming catalyst.
Commercial catalysts are available for naphtha pre-reforming processes. However, the these commercial catalysts are not very useful or effective when used in a diesel pre-reforming processes. Diesel is more prone to coke formation than naphtha. Therefore, catalytic activities are degraded rapidly in diesel pre-reforming conditions.
Catalyst development is required for diesel pre-reforming processes. In a pre-reforming process, diesel is reformed into syngas before being fed to SOFC systems. Pre-reforming is operated without an oxygen feed and at lower than 500° C. Therefore, pre-reforming has higher efficiency than other reforming methods. However, a highly active catalyst is required for diesel pre-reforming because of characteristic of diesel and low operation temperature. No commercial catalysts are currently available for diesel pre-reforming. Additionally, no commercial catalysts are available to process diesel type liquid hydrocarbons to methane rich gas that can provide high fuel conversion, selectivity, and stability.